terça-feira, 14 de setembro de 2010

Ancient fish was advanced for its age

The fish skull emerging from the rock it was found in (Image: John Broomfield/Museum Victoria)

Fish developed features characteristic of land animals much earlier than once thought, say researchers.

Dr John Long of Museum Victoria and colleagues base their conclusions on an uncrushed 380 million-year-old fish fossil found in Western Australia.

"The specimen is the most perfect complete three-dimensional fish of its kind ever discovered in the whole world," says Long, who reports the team's findings online today in the journal Nature.

"It looks like it died yesterday. You can still open and close the mouth."

Long says the preserved remains of a Gogonasus fish from the Devonian period were found last year in the remote Kimberley area at the Gogo fossil site, once an 'ancient barrier reef' teeming with fish.

But when his team used a CT scanner at the Australian National University to analyse this new fossil, it found the fish had a number of features common to land animals.

"It's hiding a lot of deceptively advanced features that were not recognised before until we had such a perfect specimen," says Long.

For example, Gogonasus had hole in its skull similar to that found in the first land animals, he says.

This hole eventually became the Eustachian tube in higher vertebrates, says Long.

His team's analysis also revealed the fish's pectoral fin had the same pattern of bones as the forelimbs or arms of land animals, called tetrapods.

"It's definitely a fish. It's got gills, it swims in water, it's got fins," says Long. "But it's a fish that is showing the beginnings of the tetrapod's advanced body plan that would eventually carry on to all living land animals."

Gogonasus also had a cheek bone structure similar to early amphibian and a single pair of nostrils, like we have, says Long.

Wolf in sheep's clothing

Earlier this year scientists reported the discovery of Tiktaalik roseae, a 375 million-year-old species of fish that filled the evolutionary gap in the transition between water and land animals.

While Tiktaalik had a skull that was identical to an amphibian, Gogonasus looks much more like a fish, says Long.

"This particular fish is a bit like a wolf in sheep's clothing," he says.